Aqueous resin based inkjet inks

ABSTRACT

An inkjet ink includes a) an aqueous medium; and b) capsules composed of a polymeric shell surrounding a core; wherein the capsules are dispersed in the aqueous medium using a dispersing group covalently bonded to the polymeric shell; wherein the core contains a photoinitiator and one or more chemical reactants capable of forming a reaction product upon application of UV light; wherein the capsules have an average particle size of no more than 4 μm as determined by dynamic laser diffraction; and wherein the photoinitiator is a diffusion hindered photoinitiator selected from the group consisting of multifunctional photoinitiators, oligomeric photoinitiators, polymeric photoinitiators and polymerizable photoinitiators.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2015/058129, filed Apr. 15, 2015. This application claims thebenefit of European Application No. 14164674.5, filed Apr. 15, 2014,which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to aqueous resin based inkjet inks, morespecifically aqueous inkjet inks containing capsules, such asmicrocapsules or nanocapsules.

2. Description of the Related Art

Over the last years, offset and flexographic printing systems are beingincreasingly replaced by industrial inkjet printing systems due to theirflexibility in use, e.g. variable data printing, and due to theirenhanced reliability allowing their incorporation into production lines.

Radiation curable inkjet inks have been the preferred choice of ink forreasons of reliability and because high quality images can be printed onnon-absorbing ink-receivers. However for economical and ecologicalreasons, it is desirable to be able to print aqueous resin based inks ina reliable way on these industrial inkjet printing systems.

It has also been observed that the required physical properties of theprinted image such as adhesion performance, scratch resistance, solventresistance, water fastness and flexibility, are much more difficult toobtain by aqueous inks compared to reactive inks.

Encapsulation is a process in which tiny particles or droplets aresurrounded by a shell to give small capsules. The material inside thecapsule is referred to as the core or the internal phase, whereas theshell is sometimes called a wall. This technology has been applied indifferent technical fields, such as self healing compositions (Blaisziket al., Annual Review of Materials, 40, 179-211 (2010)), textiletreatment (Marinkovic et al., CI&CEQ 12(1), 58-62 (2006); Nelson G.,International Journal of Pharmaceutics, 242, 55-62 (2002), Teixeira etal., AIChE Journal, 58(6), 1939-1950 (2012)), thermal energy storage andrelease for buildings (Tyagi et al., Renewable and Sustainable EnergyReviews, 15, 1373-1391 (2011)), printing and recording technology(Microspheres, Microcapsules and Liposomes: Volume 1: Preparation andChemical Applications, editor R. Arshady, 391-417 and ibid., 420-438,Citus Books, London, 1999), personal care, pharmaceuticals, nutrition,agrochemicals (Lidert Z., Delivery System Handbook for Personal Care andCosmetic Products, 181-190, Meyer R. Rosen (ed.), William Andrew, Inc.2005; Schrooyen et al., Proceedings of the Nutrition Society, 60,475-479 (2001)) and electronic applications (Yoshizawa H., KONA, 22,23-31 (2004)).

The use of encapsulation technology in ink jet inks has largely beenlimited to the design of encapsulated pigments, where a polymer shell isdirectly polymerized on the surface of the pigment particles. Forexample, US 2009227711 A (XEROX) discloses encapsulated nanoscaleparticles of organic pigments, comprising a polymer-based encapsulatingmaterial, and one or more nanoscale organic pigment particlesencapsulated by the polymer-based encapsulating material to be used ascolorants for compositions such as inks, toners and the like. Thisapproach doesn't allow boosting the physical properties needed inindustrial applications.

JP 2004075759 (FUJI) discloses an ink jet ink including a microcapsulecomprising at least one hydrophobic dye, at least one hydrophobicpolymer and at least one high boiling solvent, where the capsule wallsare prepared using a polyfunctional isocyanate compound. All theexamples disclosed require the use of an additional water solublepolymer, i.e. gelatine.

Encapsulation as an approach to integrate reactive chemistry in ink jetinks has hardly been disclosed. US 2012120146 A (XEROX) discloses acurable ink comprising microcapsules. The microcapsules contain at leastone first reactive component and at least one second componentcomprising a triggerable compound, and they are dispersed in at leastone third reactive component. After stimulus induced rupture of thecapsules, polymerisation of the ink is obtained by reaction of the atleast one first reactive component with the third reactive component.From Example 6, it should be clear that the microcapsules are integratedinto a UV curable ink rather then an aqueous based ink.

US 2014002566 A (SEIKO EPSON) discloses an inkjet ink including acoating film forming material, a polyether-modified silicone oil, andwater, resulting in micelles dispersed in an aqueous medium. In onepreferred embodiment the inkjet ink is a photocurable inkjet ink byincluding a photocurable compound in the micelles. A similar concept isdisclosed by US2011237700 A (SEIKO EPSON).

US2011261108 A (TOSHIBA TEC) discloses a decolorizable water-basedinkjet ink including a color material, a solvent, and a nonionicsurfactant, wherein the color material contains a color developablecompound and a color developing agent.

Reviewing the synthetic approaches for the synthesis of microcapsules ingeneral, it becomes clear that the use of an additional hydrophilicpolymer is required to control the colloid stability, the particle sizeand the particle size distribution, which are three critical factors forthe design of an ink jet ink. However, the use of water soluble polymersin aqueous based ink jet inks very often has a detrimental impact onjetting reliability and latency, aspects which are particularlyimportant in an industrial environment where down time and complexmaintenance cycles have to be avoided.

Therefore, there remains a need for aqueous resin based inkjet inksexhibiting good physical properties on a wide range of substrates, whileexhibiting high reliability for industrial inkjet printing.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention have been realised with an inkjet ink asdefined below.

It was found that reactive chemistry could be incorporated intoself-dispersing capsules including at least one dispersing groupcovalently coupled to the shell polymers lead to stable ink jet inkswithout the need for additional water soluble polymers. The chemicalreactants in the core of the capsules where able to form a reactionproduct upon application of UV light. A wide variety of substrates couldbe addressed, including both absorbing substrates, e.g. textiles, andnon-absorbing substrates, e.g. glass and polymeric substrates.

It was found that capsules (3) composed of a polymeric shell (4)surrounding a core (5), with the core (5) containing UV curablecompounds (16) and a photoinitiator (15) could be advantageously used inan UV curable inkjet ink. Such inkjet inks bring advantages in printingon packaging for food and pharmaceutical products, as they containroughly only a fifth of the monomers and photoinitiators presently usedby UV curable inkjet inks as disclosed in, for example, EP 2053103 A(AGFA), which makes it easier to reach the legal migration limits forfood safety.

These inkjet inks bring also advantages for the textile printingindustry where costly and laborious pre and post-treatments can beavoided. Furthermore textiles printed with UV curable inks containingthese capsules don't exhibit the detrimental effect on the look-and-feelof the textiles by the traditional UV curable inkjet inks which feelhard and plastic-like.

Further objects of the invention will become apparent from thedescription hereinafter.

Definitions

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. methyl, ethyl, for three carbon atoms:n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl andtertiary-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl,2,2-dimethylpropyl and 2-methyl-butyl, etc.

Unless otherwise specified a substituted or unsubstituted alkyl group ispreferably a C₁ to C₆-alkyl group.

Unless otherwise specified a substituted or unsubstituted alkenyl groupis preferably a C₁ to C₆-alkenyl group.

Unless otherwise specified a substituted or unsubstituted alkynyl groupis preferably a C₁ to C₆-alkynyl group.

Unless otherwise specified a substituted or unsubstituted aralkyl groupis preferably a phenyl or naphthyl group including one, two, three ormore C₁ to C₆-alkyl groups.

Unless otherwise specified a substituted or unsubstituted alkaryl groupis preferably a C₇ to C₂₀-alkyl group including a phenyl group ornaphthyl group.

Unless otherwise specified a substituted or unsubstituted aryl group ispreferably a phenyl group or naphthyl group

Unless otherwise specified a substituted or unsubstituted heteroarylgroup is preferably a five- or six-membered ring substituted by one, twoor three oxygen atoms, nitrogen atoms, sulphur atoms, selenium atoms orcombinations thereof.

The term “substituted”, in e.g. substituted alkyl group means that thealkyl group may be substituted by other atoms than the atoms normallypresent in such a group, i.e. carbon and hydrogen. For example, asubstituted alkyl group may include a halogen atom or a thiol group. Anunsubstituted alkyl group contains only carbon and hydrogen atoms

Unless otherwise specified a substituted alkyl group, a substitutedalkenyl group, a substituted alkynyl group, a substituted aralkyl group,a substituted alkaryl group, a substituted aryl and a substitutedheteroaryl group are preferably substituted by one or more constituentsselected from the group consisting of methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl and tertiary-butyl, ester group, amidegroup, ether group, thioether group, ketone group, aldehyde group,sulfoxide group, sulfone group, sulfonate ester group, sulphonamidegroup, —Cl, —Br, —I, —OH, —SH, —CN and —NO₂.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an inkjet ink (1) including an aqueous medium (2) andcapsules (3) composed of a polymeric shell (4) surrounding a core (5)containing one or more chemical reactants.

FIG. 2 gives six examples a. to g. of inkjet printing modes that can beused in accordance with the invention, wherein in a., an ink droplet(12) is jetted by an inkjet print head (6) on a substrate (10) and ajetted ink droplet (13) is dried by a dryer (7) before being irradiatedby an infrared radiation source (8) for opening the capsules and a UVcuring device (9) to cure the polymerizable compounds that wereincorporated in the core (5); in b., the infrared radiation source (8)of a. has been omitted as a UV curing device (9), e.g. a mercury bulb,is selected that emits sufficient heat radiation for opening thecapsules as well as UV curing the polymerizable compounds; in c., thedryer (7) of a. has been omitted as the infrared radiation source (8) iscapable of drying the layer and opening the capsules before a UV curingdevice (9) cures the polymerizable compounds flowing out of thecapsules; d. shows the same inkjet printing mode as in c. except that apre-heating device (11) is present for pre-heating the substrate (10);e. shows an inkjet printing mode wherein an ink droplet (12) is jettedby an inkjet print head (6) on a substrate (10) and a jetted ink dropletis dried by a UV curing device (9), e.g. a mercury bulb, emittingsufficient heat radiation for opening the capsules as well as UV curingthe polymerizable compounds flowing out of the capsules; and f. showsthe same inkjet printing mode as in e. except that a pre-heating device(11) is present for pre-heating the substrate (10).

FIG. 3 illustrates the mechanism believed to occur in three steps from Ato D. In a first step A to B, the aqueous medium (2) is removed bydrying so that capsules (3) having a polymeric shell (4) with a core (5)containing a colorant (14) and a photoinitiator (15) remain on thesubstrate (10). In the second step B to C, the capsules (3) are openedso that polymerizable compounds (18) flow from the core (5) through thepermeable polymeric shell (17). In the last step C to D, thepolymerizable compounds (18) are cured by UV radiation into apolymerized compound (18).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Inkjet Inks

The inkjet ink according to a preferred embodiment of the presentinvention includes a) an aqueous medium; and b) capsules composed of apolymeric shell surrounding a core; wherein the capsules are dispersedin the aqueous medium using a dispersing group covalently bonded to thepolymeric shell; wherein the core contains a photoinitiator and one ormore chemical reactants capable of forming a reaction product uponapplication of UV light; wherein the capsules have an average particlesize of no more than 4 μm as determined by dynamic laser diffraction;and wherein the photoinitiator is a diffusion hindered photoinitiatorselected from the group consisting of multifunctional photoinitiators,oligomeric photoinitiators, polymeric photoinitiators and polymerizablephotoinitiators.

The inkjet ink can be a colourless inkjet ink for use as a primer or avarnish, but preferably the inkjet ink contains at least one colorant.

In a preferred embodiment, the inkjet ink according to the invention ispart of an inkjet ink set, more preferably part of a multi colour inkjetink set including a plurality of inkjet inks according to the invention.The inkjet ink set preferably includes at least a cyan inkjet ink, amagenta inkjet ink, a yellow inkjet ink and a black inkjet ink. Such aCMYK-inkjet ink set may also be extended with extra inks such as red,green, blue, violet and/or orange to further enlarge the colour gamut ofthe image. The inkjet ink set may also be extended by the combination ofthe full density inkjet inks with light density inkjet inks. Thecombination of dark and light colour inks and/or black and grey inksimproves the image quality by a lowered graininess.

The inkjet ink set may also include one or more spot colours, preferablyone or more corporate colours, such as e.g. the red colour of CocaCola™.

The inkjet ink set may also include a varnish for improving the gloss oncertain substrates like textiles.

In a preferred embodiment, the inkjet ink set also includes a whiteinkjet ink. This allows obtaining more brilliant colours, especially ontransparent substrates, where the white inkjet ink can be applied eitheras a primer or on top of the colour inkjet inks when the image is viewedthrough the transparent substrate.

The viscosity of the inkjet ink is preferably smaller than 25 mPa·s at25° C. and at a shear rate of 90 s⁻¹, more preferably between 2 and 15mPa·s at 25° C. and at a shear rate of 90 s⁻¹.

The surface tension of the inkjet ink is preferably in the range ofabout 18 mN/m to about 70 mN/m at 25° C., more preferably in the rangeof about 20 mN/m to about 40 mN/m at 25° C.

The inkjet ink may also contain at least one surfactant for obtaininggood spreading characteristics on a substrate.

Capsules

The capsules have a polymeric shell surrounding a core containingreactive chemistry. The capsules are preferably present in the inkjetink in amount of no more than 27 wt %, preferably between 5 and 25 wt %based on the total weight of the inkjet ink. It was observed that above27 wt % jetting was not always so reliable.

The capsules have an average particle size of no more than 4 μm asdetermined by dynamic laser diffraction. The nozzle diameter of inkjetprint heads is usually 20 to 35 μm. Reliable inkjet printing is possibleif the average particle size of the capsules is five times smaller thanthe nozzle diameter. An average particle size of no more than 4 μmallows jetting by print heads having the smallest nozzle diameter of 20μm. In a more preferred embodiment, the average particle size of thecapsules is ten times smaller than the nozzle diameter. Hencepreferably, the average particle size is from 0.05 to 2 μm, morepreferably from 0.10 to 1 μm. When the average particle size of thecapsule is smaller than 2 μm, excellent resolution and dispersionstability with time are obtained.

The capsules are dispersed in the aqueous medium of the inkjet ink usinga dispersing group covalently bonded to the polymeric shell. Thedispersing group is preferably selected from the group consisting of acarboxylic acid or salt thereof, a sulfonic acid or salt thereof, aphosphoric acid ester or salt thereof, a phosphonic acid or saltthereof, an ammonium group, a sulfonium group, a phosphonium group and apolyethylene oxide group.

The dispersing group can be used in combination with a polymericdispersant in order to accomplish steric stabilization. For example, thepolymeric shell may have covalently bonded carboxylic acid groups thatinteract with amine groups of a polymeric dispersant. However, in a morepreferred embodiment, no polymeric dispersant is used and dispersionstability of the inkjet ink is accomplished solely by electrostaticstabilization. For example, a slightly alkaline aqueous medium will turnthe carboxylic acid groups covalently bonded polymeric shell into ionicgroups, whereafter the negatively charged capsules have no tendency toagglomerate. If sufficient dispersing groups are covalently bonded tothe polymeric shell, the capsule becomes a so-called self-dispersingcapsule.

These negatively or positively charged capsule surfaces can also beadvantageously used during inkjet printing. For example, a second liquidcontaining a cationic substance, such as a compound containing ammoniumgroups, can be used to precipitate capsules and, if polymeric ormultivalent cations are used, to bind capsules together by interactionwith the dissociated carboxylic acid groups covalently bonded to thepolymeric shell. By using this method an improvement in image qualitycan be observed due to the immobilisation of the capsules.

There is no real limitation on the type of polymer used for thepolymeric shell of the capsule. Preferably, the polymer used in thepolymeric shell is preferably crosslinked. By crosslinking, morerigidity is built into the capsules allowing a broader range oftemperatures and pressures for handling the capsules in both the inkmaking and in the inkjet printer.

Preferred examples of the polymeric shell material include polyureas,polyurethanes, polyesters, polycarbonates, polyamides, melamine basedpolymers and mixtures thereof, with polyureas and polyurethanes beingespecially preferred.

Capsules can be prepared using both chemical and physical methods.Suitable encapsulation methodologies include complex coacervation,liposome formation, spray drying and polymerization methods.

In a preferred embodiment of the present invention preferably apolymerization method is used, as it allows the highest control indesigning the capsules. More preferably interfacial polymerization isused to prepare the capsules used in the invention. This technique iswell-known and has recently been reviewed by Zhang Y. and Rochefort D.(Journal of Microencapsulation, 29(7), 636-649 (2012) and by Salitin (inEncapsulation Nanotechnologies, Vikas Mittal (ed.), chapter 5, 137-173(Scrivener Publishing LLC (2013)).

Interfacial polymerisation is a particularly preferred technology forthe preparation of capsules according to a preferred embodiment of thepresent invention. In interfacial polymerization, such as interfacialpolycondensation, two reactants meet at the interface of the emulsiondroplets and react rapidly.

In general, interfacial polymerisation requires the dispersion of anoleophilic phase in an aqueous continuous phase or vice versa. Each ofthe phases contains at least one dissolved monomer (a first shellcomponent) that is capable of reacting with another monomer (a secondshell component) dissolved in the other phase. Upon polymerisation, apolymer is formed that is insoluble in both the aqueous and theoleophilic phase. As a result, the formed polymer has a tendency toprecipitate at the interface of the oleophilic and aqueous phase, herebyforming a shell around the dispersed phase, which grows upon furtherpolymerisation. The capsules according to a preferred embodiment of thepresent invention are preferably prepared from an oleophilic dispersionin an aqueous continuous phase.

Typical polymeric shells, formed by interfacial polymerisation areselected from the group consisting of polyamides, typically preparedfrom di- or oligoamines as first shell component and di- or poly-acidchlorides as second shell component, polyurea, typically prepared fromdi- or oligoamines as first shell component and di- or oligoisocyanatesas second shell component, polyurethanes, typically prepared from di- oroligoalcohols as first shell component and di- or oligoisocyanates assecond shell component, polysulfonamides, typically prepared from di- oroligoamines as first shell component and di- or oligosulfochlorides assecond shell component, polyesters, typically prepared from di- oroligoalcohols as first shell component and di- or oligo-acid chloridesas second shell component and polycarbonates, typically prepared fromdi- or oligoalcohols as first shell component and di- oroligo-chloroformates as second shell component. The shell can becomposed of combinations of these polymers.

In a further preferred embodiment, polymers, such as gelatine, chitosan,albumin and polyethylene imine can be used as first shell components incombination with a di- or oligo-isocyanate, a di- or oligo acidchloride, a di- or oligo-chloroformate and an epoxy resin as secondshell component.

In a particularly preferred embodiment, the shell is composed of apolyurethane, a polyurea or a combination thereof. In a furtherpreferred embodiment, a water immiscible solvent is used in thedispersion step, which is removed by solvent stripping before or afterthe shell formation. In a particularly preferred embodiment, the waterimmiscible solvent has a boiling point below 100° C. at normal pressure.Esters are particularly preferred as water immiscible solvent.

A water immiscible solvent is an organic solvent having low miscibilityin water. Low miscibility is defined as any water solvent combinationforming a two phase system at 20° C. when mixed in a one over one volumeratio.

The core contains one or more chemical reactants capable of forming areaction product upon application of UV light. These one or morechemical reactants, here below also referred to as the “reactivechemistry”, are usually incorporated into the capsules by dissolving itin an organic solvent having low miscibility with water and having alower boiling point than water. A preferred organic solvent is ethylacetate, because it also has a low flammability hazard compared to otherorganic solvents.

However, in some cases the organic solvent may be omitted. For example,the organic solvent can be omitted when liquid reactive components, morepreferably free radical curable or cationic curable monomers oroligomers having a viscosity of less then 100 mPa·s, are used aschemical reactant in the capsules.

The method for preparing a dispersion of capsules preferably includesthe following steps:

-   a) preparing a non-aqueous solution of a first reactant for forming    the polymeric shell and the one or more chemical reactants    optionally in an organic solvent having a low miscibility with water    and having a lower boiling point than water;-   b) preparing an aqueous solution of a second reactant for forming    the polymeric shell;-   c) dispersing the non-aqueous solution under high shear in the    aqueous solution;-   d) optionally stripping the organic solvent from the mixture of the    aqueous solution and the non-aqueous solution; and-   e) preparing a polymeric shell around the one or more chemical    reactants by interfacial polymerization of the first and second    reactants for forming the polymeric shell.

The capsule dispersion can then be completed into an inkjet ink byaddition of e.g. water, humectants, surfactant and the like.

Other additives may be included into the core of the capsule such as,for example, light stabilizers, conductive particles and polymers,magnetic particles, or other compounds suitable for the specificapplication for which the inkjet ink is used.

Light Curable Reactive Chemistry

The reactive chemistry in the core is responsive to UV light. UV curablereactive chemistry contains one or more chemical reactants, such as amonomer, oligomer or polymer, which are curable by free radicalpolymerization or by cationic polymerization. In a preferred embodiment,the monomer, oligomer or polymer includes at least one acrylate group aspolymerizable group.

In addition to the monomer, oligomer or polymer that are curable by freeradical polymerization or by cationic polymerization in the core of thecapsule, water soluble monomers and oligomers may also be included intothe aqueous medium.

The inkjet ink preferably includes at least one photoinitiator. Althoughwater soluble or water dispersible photoinitiators may be used in theaqueous medium, preferably the at least one photoinitiator is present inthe core of the capsule. Preferably also at least one co-initiator ispresent in the inkjet ink. Similarly the at least one co-initiator maybe present in the aqueous medium, but is preferably present in the coreof the capsule

Any polymerizable compound commonly known in the art may be employed. Acombination of monomers, oligomers and/or polymers may be used. Themonomers, oligomers and/or polymers may possess different degrees offunctionality, and a mixture including combinations of mono-, di-, tri-and higher functionality monomers, oligomers and/or polymers may beused.

Particularly preferred for use as a free radical curable compound in theinkjet ink are monofunctional and/or polyfunctional acrylate monomers,oligomers or prepolymers, such as isoamyl acrylate, stearyl acrylate,lauryl acrylate, octyl acrylate, decyl acrylate, isoamylstyl acrylate,isostearyl acrylate, 2-ethylhexyl-diglycol acrylate, 2-hydroxybutylacrylate, 2-acryloyloxyethylhexahydrophthalic acid, butoxyethylacrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycolacrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycolacrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornylacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,2-hydroxy-3-phenoxypropyl acrylate, vinyl ether acrylate,2-acryloyloxyethylsuccinic acid, 2-acryloyxyethylphthalic acid,2-acryloxyethyl-2-hydroxyethyl-phthalic acid, lactone modified flexibleacrylate, and t-butylcyclohexyl acrylate, triethylene glycol diacrylate,tetraethylene glycol diacrylate, polyethylene glycol diacrylate,dipropylene glycol diacrylate, tripropylene glycol diacrylate,polypropylene glycol diacrylate, 1,4-butanediol diacrylate,1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycoldiacrylate, dimethylol-tricyclodecane diacrylate, bisphenol A EO(ethylene oxide) adduct diacrylate, bisphenol A PO (propylene oxide)adduct diacrylate, hydroxypivalate neopentyl glycol diacrylate,propoxylated neopentyl glycol diacrylate, alkoxylateddimethyloltricyclodecane diacrylate and polytetramethylene glycoldiacrylate, trimethylolpropane triacrylate, EO modifiedtrimethylolpropane triacrylate, tri (propylene glycol) triacrylate,caprolactone modified trimethylolpropane triacrylate, pentaerythritoltriacrylate, pentaerithritol tetraacrylate, pentaerythritolethoxytetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropanetetraacrylate, glycerinpropoxy triacrylate, and caprolactam modifieddipentaerythritol hexaacrylate, or an N-vinylamide such as,N-vinylcaprolactam or N-vinylformamide; or acrylamide or a substitutedacrylamide, such as acryloylmorpholine.

Other suitable monofunctional acrylates include caprolactone acrylate,cyclic trimethylolpropane formal acrylate, ethoxylated nonyl phenolacrylate, isodecyl acrylate, isooctyl acrylate, octyldecyl acrylate,alkoxylated phenol acrylate, tridecyl acrylate and alkoxylatedcyclohexanone dimethanol diacrylate.

Other suitable difunctional acrylates include alkoxylated cyclohexanonedimethanol diacrylate, alkoxylated hexanediol diacrylate, dioxane glycoldiacrylate, dioxane glycol diacrylate, cyclohexanone dimethanoldiacrylate, diethylene glycol diacrylate and neopentyl glycoldiacrylate.

Other suitable trifunctional acrylates include propoxylated glycerinetriacrylate and ethoxylated or propoxylated trimethylolpropanetriacrylate.

Other higher functional acrylates include di-trimethylolpropanetetraacrylate, dipentaerythritol pentaacrylate, ethoxylatedpentaeryhtitol tetraacrylate, methoxylated glycol acrylates and acrylateesters.

Furthermore, methacrylates corresponding to the above-mentionedacrylates may be used with these acrylates. Of the methacrylates,methoxypolyethylene glycol methacrylate, methoxytriethylene glycolmethacrylate, hydroxyethyl methacrylate, phenoxyethyl methacrylate,cyclohexyl methacrylate, tetraethylene glycol dimethacrylate, andpolyethylene glycol dimethacrylate are preferred due to their relativelyhigh sensitivity and higher adhesion to an ink-receiver surface.

Furthermore, the inkjet ink may also contain polymerizable oligomers.Examples of these polymerizable oligomers include epoxy acrylates,aliphatic urethane acrylates, aromatic urethane acrylates, polyesteracrylates, and straight-chained acrylic oligomers.

Suitable examples of styrene compounds are styrene, p-methylstyrene,p-methoxystyrene, b-methylstyrene, p-methyl-b-methylstyrene,a-methylstyrene and p-methoxy-b-methylstyrene.

Suitable examples of vinylnaphthalene compounds are 1-vinylnaphthalene,a-methyl-1-vinylnaphthalene, b-methyl-1-vinylnaphthalene,4-methyl-1-vinylnaphthalene and 4-methoxy-1-vinylnaphthalene.

Suitable examples of N-vinyl heterocyclic compounds areN-vinylcarbazole, N-vinylpyrrolidone, N-vinylindole, N-vinylpyrrole,N-vinylphenothiazine, N-vinylacetoanilide, N-vinylethylacetoamide,N-vinylsuccinimide, N-vinylphthalimide, N-vinylcaprolactam andN-vinylimidazole.

In a preferred embodiment, the free curable compound in the inkjet inkincludes at least one monomer selected from the group consisting ofN-vinyl caprolactam, phenoxyethyl acrylate, dipropyleneglycoldiacrylate,ethoxylated trimethylolpropane triacrylate, pentaerythritoltetraacrylate, and cyclic trimethylolpropane formal acrylate.

The polymerizable compound may also be a cationically polymerizablecompound. Suitable examples of cationically curable compounds can befound in Advances in Polymer Science, 62, pages 1 to 47 (1984) by J. V.Crivello.

The cationic curable compound may contain at least one olefin,thioether, acetal, thioxane, thietane, aziridine, N, O, S or Pheterocycle, aldehyde, lactam or cyclic ester group.

Examples of cationic polymerizable compounds include monomers and/oroligomers epoxides, vinyl ethers, styrenes, oxetanes, oxazolines,vinylnaphthalenes, N-vinyl heterocyclic compounds, tetrahydrofurfurylcompounds.

Suitable cationic curable compounds having at least one epoxy group arelisted in the “Handbook of Epoxy Resins” by Lee and Neville, McGraw HillBook Company, New York (1967) and in “Epoxy Resin Technology” by P. F.Bruins, John Wiley and Sons New York (1968).

Examples of cationic curable compounds having at least one epoxy groupinclude 1,4-butanediol diglycidyl ether,3-(bis(gycidyloxymethyl)methoxy)-1,2-propane diol, limonene oxide,2-biphenyl gycidyl ether,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate,epichlorohydrin-bisphenol S based epoxides, epoxidized styrenics andmore epichlorohydrin-bisphenol F and A based epoxides and epoxidizednovolaks.

Suitable epoxy compounds comprising at least two epoxy groups in themolecule are alicyclic polyepoxide, polyglycidyl ester of polybasicacid, polyglycidyl ether of polyol, polyglycidyl ether ofpolyoxyalkylene glycol, polyglycidyl ester of aromatic polyol,polyglycidyl ether of aromatic polyol, urethane polyepoxy compound, andpolyepoxy polybutadiene.

Examples of cycloaliphatic diepoxides include copolymers of epoxides andhydroxyl components such as glycols, polyols, or vinyl ether, such as3,4-epoxycyclohexylmethyl-3′, 4′-epoxycyclohexylcarboxylate; bis(3,4-epoxycylohexylmethyl) adipate; limonene diepoxide; diglycidyl esterof hexahydrophthalic acid.

Examples of vinyl ethers having at least one vinyl ether group includeethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecylvinyl ether, cyclohexyl vinyl ether, butanediol divinyl ether, hydroxylbutyl vinyl ether, cyclohexane dimethanol monovinyl ether, phenyl vinylether, p-methylphenyl vinyl ether, p-methoxyphenyl vinyl ether,a-methylphenyl vinyl ether, b-methylisobutyl vinyl ether andb-chloroisobutyl vinyl ether, diethyleneglycol divinyl ether,triethylene glycol divinyl ether, n-propyl vinyl ether, isopropyl vinylether, dodecyl vinyl ether, diethylene glycol monovinyl ether,cyclohexanedimethanol divinyl ether, 4-(vinyloxy)butyl benzoate,bis[4-(vinyl oxy)butyl]adipate, bis[4-(vinyl oxy)butyl]succinate,4-(vinyloxy methyl) cyclohexylmethyl benzoate,bis[4-(vinyloxy)butyl]isophthalate,bis[4-(vinyloxymethyl)cyclohexylmethyl]glutarate,tris[4-(vinyloxy)butyl]trimellitate,4-(vinyloxy)butyl steatite,bis[4-(vinyloxy)butyl]hexanediylbiscarbamate,bis[4-(vinyloxy)methyl]cyclohexyl]methyl]terephthalate,bis[4-(vinyloxy)methyl]cyclohexyl]methyl]isophthalate,bis[4-(vinyloxy)butyl](4-methyl-1,3-phenylene)-biscarbamate,bis[4-vinyloxy)butyl](methylenedi-4,1-phenylene) biscarbamate and3-amino-1-propanol vinyl ether.

Suitable examples of oxetane compounds having at least one oxetane groupinclude 3-ethyl-3-hydroloxymethyl-1-oxetane, the oligomeric mixture1,4-bis [3-ethyl-3-oxetanyl methoxy)methyl]benzene,3-ethyl-3-phenoxymethyl-oxetane, bis ([1-ethyl(3-oxetanil)]methyl)ether, 3-ethyl-3-[(2-ethylhexyloxy) methyl]oxetane,3-ethyl-[(tri-ethoxysilyl propoxy)methyl]oxetane and3,3-dimethyl-2(p-methoxy-phenyl)-oxetane

If the one or more chemical reactants in the core of the capsule are oneor more free radical curable compounds, then the photoinitiator is aNorrish Type I or II photoinitiator. If the one or more chemicalreactants in the core of the capsule are one or more cationicallycurable compounds, then the photoinitiator is a cationic photoinitiator.

The photoinitiator is preferably a free radical initiator. Two types offree radical photoinitiators can be distinguished and used in the inkjetinks of a preferred embodiment of the present invention. A Norrish TypeI initiator is an initiator which cleaves after excitation, yielding theinitiating radical immediately. A Norrish type II-initiator is aphotoinitiator which is activated by actinic radiation and forms freeradicals by hydrogen abstraction from a second compound that becomes theactual initiating free radical. This second compound is called apolymerization synergist or co-initiator. Both type I and type IIphotoinitiators can be used in the present invention, alone or incombination.

Suitable photo-initiators are disclosed in CRIVELLO, J. V., et al.VOLUME III: Photoinitiators for Free Radical Cationic. 2nd edition.Edited by BRADLEY, G. London, UK: John Wiley and Sons Ltd, 1998. p.287-294.

Specific examples of photo-initiators may include, but are not limitedto, the following compounds or combinations thereof: benzophenone andsubstituted benzophenones, 1-hydroxycyclohexyl phenyl ketone,thioxanthones such as isopropylthioxanthone,2-hydroxy-2-methyl-1-phenylpropan-1-one,2-benzyl-2-dimethylamino-(4-morpholinophenyl) butan-1-one, benzildimethylketal, bis (2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphineoxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide,2-methyl-1-[4-(methylthio) phenyl]-2-morpholinopropan-1-one,2,2-dimethoxy-1, 2-diphenylethan-1-one or5,7-diiodo-3-butoxy-6-fluorone.

Suitable commercial photo-initiators include Irgacure™ 184, Irgacure™500, Irgacure™ 907, Irgacure™ 369, Irgacure™ 1700, Irgacure™ 651,Irgacure™ 819, Irgacure™ 1000, Irgacure™ 1300, Irgacure™ 1870, Darocur™1173, Darocur™ 2959, Darocur™ 4265 and Darocur™ ITX available from CIBASPECIALTY CHEMICALS, Lucerin™ TPO available from BASF AG, Esacure™KT046, Esacure™ KIP150, Esacure™ KT37 and Esacure™ EDB available fromLAMBERTI, H-Nu™ 470 and H-Nu™ 470X available from SPECTRA GROUP Ltd.

For safety reasons, the photoinitiator is preferably a so-calleddiffusion hindered photoinitiator. A diffusion hindered photoinitiatoris a photoinitiator which exhibits a much lower mobility in a curedlayer of the curable inkjet ink than a monofunctional photoinitiator,such as benzophenone. Several methods can be used to lower the mobilityof the photoinitiator. One way is to increase the molecular weight ofthe photoinitiator so that the diffusion speed is reduced, e.g.polymeric photoinitiators. Another way is to increase its reactivity sothat it is built into the polymerizing network, e.g. multifunctionalphotoinitiators (having 2, 3 or more photoinitiating groups) andpolymerizable photoinitiators. The diffusion hindered photoinitiator ispreferably selected from the group consisting of multifunctionalphotoinitiators, oligomeric photoinitiators, polymeric photoinitiatorsand polymerizable photoinitiators. Most preferably the diffusionhindered photoinitiator is a polymerizable initiator or a polymericphotoinitiator.

Suitable diffusion hindered photoinitiators are also those disclosed inEP 2053101 A (AGFA) in paragraphs [0074] and [0075] for difunctional andmultifunctional photoinitiators, in paragraphs [0077] to [0080] forpolymeric photoinitiators and in paragraphs [0081] to [0083] forpolymerizable photoinitiators.

Other preferred polymerizable photoinitiators are those disclosed in EP2065362 A (AGFA) and EP 2161264 A (AGFA), incorporated herein byreference.

If the core of the capsule contains one or more cationically radicalcurable compounds, then the core contains at least one cationicphotoinitiator. A cationic photoinitiator is a compound that generatesacid and initiates cationic polymerization upon irradiation by UV light.Any known cationic photoinitiator may be used. The cationicphotoinitiator may be used alone as a single initiator or as a mixtureof two or more initiators.

Suitable photocationic polymerization initiators include diazoniumsalts, phosphonium salts, sulfonium salts, iodonium salts, imidesulfonates, oxime sulfonates, diazo disulfones, disulfones, ando-nitrobenzyl sulfonates. Examples of these cationic photoinitiators aredescribed in US 2006222832 A (FUJI), U.S. Pat. No. 3,779,778 (3M) and US2008055379 A (KONICA).

A preferred amount of the one or more free radical and/or cationicphotoinitiators is 0-30 wt %, more preferably 0.1-20 wt %, and mostpreferably 0.3-15 wt % of the total weight of the polymerizablecomposition.

In order to increase the photosensitivity further, the free radicalcurable inkjet ink may additionally contain co-initiators. Suitableexamples of co-initiators can be categorized in three groups:

-   (1) tertiary aliphatic amines such as methyldiethanolamine,    dimethylethanolamine, triethanolamine, triethylamine and    N-methylmorpholine;-   (2) aromatic amines such as amylparadimethylaminobenzoate,    2-n-butoxyethyl-4-(dimethylamino) benzoate,    2-(dimethylamino)ethylbenzoate, ethyl-4-(dimethylamino)benzoate, and    2-ethylhexyl-4-(dimethylamino)benzoate; and-   (3) (meth)acrylated amines such as dialkylamino alkyl(meth)acrylates    (e.g., diethylaminoethylacrylate) or    N-morpholinoalkyl-(meth)acrylates (e.g.,    N-morpholinoethyl-acrylate).    Preferred Co-initiators are Aminobenzoates.

The one or more co-initiators included into the radiation curable inkjetink are preferably diffusion hindered co-initiators for safety reasons.A diffusion hindered co-initiator is preferably selected from the groupconsisting of non-polymeric di- or multifunctional co-initiators,oligomeric or polymeric co-initiators and polymerizable co-initiators.More preferably the diffusion hindered co-initiator is selected from thegroup consisting of polymeric co-initiators and polymerizableco-initiators.

The free radical curable inkjet ink preferably comprises a co-initiatorin an amount of 0.1 to 50 wt %, more preferably in an amount of 0.5 to25 wt %, most preferably in an amount of 1 to 10 wt % of the totalweight of the polymerizable composition

The free radical curable inkjet ink may further also contain at leastone inhibitor for improving the thermal stability of the polymerizablecomposition in the core of the capsule.

Suitable polymerization inhibitors include phenol type antioxidants,hindered amine light stabilizers, phosphor type antioxidants,hydroquinone monomethyl ether commonly used in (meth)acrylate monomers,and hydroquinone, t-butylcatechol, pyrogallol,2,6-di-tert.butyl-4-methylphenol (=BHT) may also be used.

Suitable commercial inhibitors are, for example, Sumilizer™ GA-80,Sumilizer™ GM and Sumilizer™ GS produced by Sumitomo Chemical Co. Ltd.;Genorad™ 16, Genorad™18 and Genorad™ 20 from Rahn AG; Irgastab™ UV10 andIrgastab™ UV22, Tinuvin™ 460 and CGS20 from Ciba Specialty Chemicals;Floorstab™ UV range (UV-1, UV-2, UV-5 and UV-8) from Kromachem Ltd,Additol™ S range (S100, S110, S120 and S130) from Cytec SurfaceSpecialties.

The inhibitor is preferably a polymerizable inhibitor.

Since excessive addition of these polymerization inhibitors may lowerthe curing speed, it is preferred that the amount capable of preventingpolymerization is determined prior to blending. The amount of apolymerization inhibitor is preferably lower than 5 wt %, morepreferably lower than 3 wt % of the total free radical or cationicallycurable composition.

Aqueous Medium

The capsules are dispersed into an aqueous medium. The aqueous mediummay consist of water, but preferably include one or more organicsolvents. Other compounds, such as e.g. monomers and oligomers,surfactants, colorants, alkaline compounds and light stabilizers, may bedissolved or dispersed in the aqueous medium.

The one or more organic solvents may be added for a variety of reasons.For example, it can be advantageous to add a small amount of an organicsolvent to improve the dissolution of a compound in the aqueous medium.

The aqueous medium may contain at least one humectant to prevent theclogging of the nozzle, due to its ability to slow down the evaporationrate of inkjet ink, especially the water in the inkjet ink. Thehumectant is an organic solvent having a higher boiling point thanwater.

Suitable humectants include triacetin, N-methyl-2-pyrrolidone, glycerol,urea, thiourea, ethylene urea, alkyl urea, alkyl thiourea, dialkyl ureaand dialkyl thiourea, diols, including ethanediols, propanediols,propanetriols, butanediols, pentanediols, and hexanediols; glycols,including propylene glycol, polypropylene glycol, ethylene glycol,polyethylene glycol, diethylene glycol, tetraethylene glycol, andmixtures and derivatives thereof. A preferred humectant is glycerol.

The humectant is preferably added to the ink-jet ink formulation in anamount of 0.1 to 20 wt % based on the total weight of the inkjet ink.

The aqueous medium preferably includes at least one surfactant. Thesurfactant can be anionic, cationic, non-ionic, or zwitter-ionic and ispreferably added in an amount below 10 wt %, more preferably below 5 wt% based on the total inkjet ink weight.

Suitable surfactants include fatty acid salts, ester salts of a higheralcohol, alkylbenzene sulphonate salts, sulphosuccinate ester salts andphosphate ester salts of a higher alcohol (e.g. sodiumdodecylbenzenesulphonate and sodium dioctylsulphosuccinate), ethyleneoxide adducts of a higher alcohol, ethylene oxide adducts of analkylphenol, ethylene oxide adducts of a polyhydric alcohol fatty acidester, and acetylene glycol and ethylene oxide adducts thereof (forexample, polyoxyethylene nonylphenyl ether, and SURFYNOL™ 104, 440, 465and TG available from AIR PRODUCTS & CHEMICALS INC.

A biocide may be added to the aqueous medium to prevent unwantedmicrobial growth, which may occur in the ink-jet ink over time. Thebiocide may be used either singly or in combination.

Suitable biocides for the ink-jet ink include sodium dehydroacetate,2-phenoxyethanol, sodium benzoate, sodium pyridinethion-1-oxide, ethylp-hydroxybenzoate and 1,2-benzisothiazolin-3-one and salts thereof.

Preferred biocides are Proxel™ GXL and Proxel™ Ultra 5 available fromARCH UK BIOCIDES and Bronidox™ available from COGNIS.

A biocide is preferably added to the aqueous medium in an amount of0.001 to 3 wt. %, more preferably 0.01 to 1.0 wt. %, each based on theinkjet ink.

The aqueous medium may further comprise at least one thickener forviscosity regulation in the inkjet ink.

Suitable thickeners include urea or urea derivatives,hydroxyethylcellulose, carboxymethylcellulose, hydroxypropylcellulose,derived chitin, derived starch, carrageenan, pullulan, proteins,poly(styrenesulphonic acid), poly(styrene-co-maleic anhydride),poly(alkyl vinyl ether-co-maleic anhydride), polyacrylamid, partiallyhydrolyzed polyacrylamid, poly(acrylic acid), poly(vinyl alcohol),partially hydrolyzed poly(vinyl acetate), poly(hydroxyethyl acrylate),poly(methyl vinyl ether), polyvinylpyrrolidone, poly(2-vinylpyridine),poly(4-vinylpyridine) and poly(diallyldimethylammonium chloride).

The thickener is added preferably in an amount of 0.01 to 20 wt %, morepreferably 0.1 to 10 wt % based on the inkjet ink.

The inkjet ink may further comprise at least one antioxidant forimproving the storage stability of an image.

As the antioxidant for improving storage stability of an image, variousorganic and metal complex type fading preventives can be used in theinvention. Organic fading preventives include hydroquinones,alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes,coumarones, alkoxyanilines and heterocycles, while metal complexesinclude nickel complexes and zinc complexes. More specifically,compounds as described in “Research Disclosure, No. 17643, VII, SectionI or J, No. 15162, No. 18716, left column on page 650, No. 36544, page527, No. 307105, page 872, and the patent cited in No. 15162, andcompounds embraced in the formula of the typical compounds and compoundexamples described on pages 127 to 137 of JP 62215272 A (FUJI).

The stabilizer is added in an amount of 0.1 to 30 wt %, preferably 1 to10 wt % based on the total weight of the inkjet ink.

The aqueous medium may contain at least one pH adjuster. Suitable pHadjusters include organic amines, NaOH, KOH, NEt₃, NH₃, HCl, HNO₃ andH₂SO₄. In a preferred embodiment, the inkjet ink has a pH higher than 7.A pH of 7, 8 or more can advantageously influence the electostaticstabilization of the capsules, especially when the dispersing groups arecarboxylic acid groups.

The aqueous medium may also includes polymeric latex particles. There isno limitation on the type of polymeric latex used in the aqueous medium.The polymer latex is preferably a self-dispersible latex, i.e. havingionic or ionizable groups such as e.g. the dispersing groups of thecapsules.

The polymer latex may be selected from an acrylate based latex, astyrene based latex, polyester based latex, and a polyurethane basedlatex. The polymer latex is preferably a polyurethane latex, morepreferably a self-dispersible polyurethane latex. The term “polyurethanebased” means that the majority of the polymer in the polymer latexconsists of polyurethane. Preferably at least 50 wt %, more preferablyat least 70 wt % of the polymer in the polyurethane latex consists ofpolyurethane.

In a particularly preferred embodiment, the aqueous medium containsinter-crosslinkable latex particles, more preferably inter-crosslinkablepolyurethane based latex particles.

Suitable examples of inter-crosslinkable latex particles are disclosedby EP 2467434 A (HP), however preferably the inter-crosslinking isobtained using (meth)acrylate groups, especially when the reactivechemistry in the core of the capsules is UV curable reactive chemistry.

Preferably a crosslinker is used to crosslink the polymerized monomersof the latex particles in order to enhance the durability of the latexparticle. The crosslinker may be a separate compound or can be across-linking monomer. For example, in a (partly) acrylate based latex,the crosslinker may be a polyfunctional monomer or oligomers such as,without limitation, ethylene glycol dimethacrylate, diethylene glycoldimethacrylate, ethylene glycol diacrylate, diethylene glycoldiacrylate, 1,6-hexanediol diacrylate, tetraethylene glycol diacrylate,tripropylene glycol diacrylate, ethoxylated bisphenol A diacrylate,pentaerythritol tri- and tetraacrylate, N,N′-methylenebisacrylamide,divinylbenzene, and mixtures thereof. When present, the crosslinkerspreferably comprise from 0.1 wt % to 15 wt % of the polymerizedmonomers.

The polymer latex in the invention is preferably a self-dispersingpolymer latex, and more preferably a self-dispersing polymer latexhaving a carboxyl group. A self-dispersing polymer latex means that itdoes not require a free emulsifier and that they can get into adispersed state in an aqueous medium even in the absence of othersurfactants due to a functional group, preferably an acidic group or asalt thereof, covalently bonded tot the latex. In preparing aself-dispersing polymer latex, preferably a monomer is used containing acarboxylic acid group, a sulfonic acid group or a phosphoric acid group.

Specific examples of the unsaturated carboxylic acid monomer includeacrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleicacid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid. Specific examples of the unsaturated sulfonic acidmonomer include styrene sulfonic acid, 2-acrylamido-2-methyl propanesulfonic acid, 3-sulfopropyl (meth)acrylate, andbis-(3-sulfopropyl)-itaconate. Specific examples of the unsaturatedphosphoric acid monomer include vinyl phosphoric acid, vinyl phosphate,bis(methacryloxyethyl)phosphate, diphenyl-2-acryloyloxyethyl phosphate,diphenyl-2-methacryloyloxyethyl phosphate, anddibutyl-2-acryloyloxyethyl phosphate.

The latex preferably has a glass transition temperature (Tg) of no morethan 70° C., more preferably no more than 50° C.

The minimum film-forming temperature (MFT) of the polymer latex ispreferably between −50 and 70° C., more preferably between −40 and 50°C.

The average particle size of the latex particles in the inkjet ink ispreferably less than 300 nm, more preferably less than 200 nm asmeasured by laser diffraction, e.g. using a Beckman Coulter™ LS 13320.

Colorants

The colorants used in the inkjet ink may be dyes, pigments or acombination thereof. Organic and/or inorganic pigments may be used.

The colorant for use is not particularly limited, and may be selectedproperly from various known colorants according to applications. Forexample, use of a pigment is preferable for forming an image superior inlight fading and weather resistance. On the contrary, use of a dye ispreferable, for forming an image superior in transparency on atransparent film. Either a water- or oil-soluble dye may be used as thedye. Preferably the dye is an oil-soluble dye because it can beincorporated in the core of the capsule, and exhibited a much betterwater resistance than images printed with water soluble dyes in theaqueous medium. In fact it has been observed that colorants, such asdisperse dyes, are well protected when incorporated into the core of thecapsule even against aggressive chemicals like hypochlorite. The lattercan be exploited in inkjet printing on textiles for allowing thoroughcleaning with concentrated detergents.

The colorant is preferably a pigment or a polymeric dye for reasons oflight fastness.

The pigments may be black, white, cyan, magenta, yellow, red, orange,violet, blue, green, brown, mixtures thereof, and the like. A colourpigment may be chosen from those disclosed by HERBST, Willy, et al.Industrial Organic Pigments, Production, Properties, Applications. 3rdedition. Wiley-VCH, 2004. ISBN 3527305769.

Suitable pigments are disclosed in paragraphs [0128] to [0138] of WO2008/074548 (AGFA GRAPHICS).

An advantage of including the pigments in the core of the capsule, isthat high dispersion stability of the pigment is not really necessary asthe dispersion stability is accomplished by the capsules in the inkjetink. As long as pigments are dispersed sufficiently to be handled in thecapsule formation process, there is no need to optimize dispersionstability.

Alternatively the pigment particles can be included in the aqueousmedium. The colour pigment can be dispersed using a polymericdispersant, but preferably a self-dispersible pigment is used. Thelatter prevents interaction of the polymeric dispersant with thedispersing groups of the capsules in the inkjet ink, since dispersionstability of the pigment is accomplished by the same technique ofelectrostatic stabilization as employed for the capsules.

A self-dispersible pigment is a pigment having on its surface covalentlybonded anionic or cationic hydrophilic groups, such as salt-forminggroups or the same groups used as dispersing groups for the capsules,that allow the pigment to be dispersed in an aqueous medium withoutusing a surfactant or a resin.

The technology for making self-dispersible pigments is well-known. Forexample, EP 1220879 A (CABOT) discloses pigments having attached a) atleast one steric group and b) at least one organic ionic group and atleast one amphiphilic counterion, wherein the amphiphilic counterion hasa charge opposite to that of the organic ionic group that are suitablefor inkjet inks. Also EP 906371 A (CABOT) discloses suitablesurface-modified coloured pigment having attached hydrophilic organicgroups containing one or more ionic groups or ionizable groups. Suitablecommercially available self-dispersible colour pigments are, forexample, the CAB-O-JET™ inkjet colorants from CABOT.

Pigment particles in inkjet inks should be sufficiently small to permitfree flow of the ink through the inkjet-printing device, especially atthe ejecting nozzles. It is also desirable to use small particles formaximum colour strength and to slow down sedimentation.

The average pigment particle size is preferably between 0.050 and 1 μm,more preferably between 0.070 and 0.300 μm and particularly preferablybetween 0.080 and 0.200 μm. Most preferably, the numeric average pigmentparticle size is no larger than 0.150 μm. The average particle size ofpigment particles is determined with a Brookhaven Instruments ParticleSizer BI90plus based upon the principle of dynamic light scattering. Theink is diluted with ethyl acetate to a pigment concentration of 0.002 wt%. The measurement settings of the BI90plus are: 5 runs at 23° C., angleof 90°, wavelength of 635 nm and graphics=correction function

However for white pigment inkjet inks, the numeric average particlediameter of the white pigment is preferably from 50 to 500 nm, morepreferably from 150 to 400 nm, and most preferably from 200 to 350 nm.Sufficient hiding power cannot be obtained when the average diameter isless than 50 nm, and the storage ability and the jet-out suitability ofthe ink tend to be degraded when the average diameter exceeds 500 nm.The determination of the numeric average particle diameter is bestperformed by photon correlation spectroscopy at a wavelength of 633 nmwith a 4 mW HeNe laser on a diluted sample of the pigmented inkjet ink.A suitable particle size analyzer used was a Malvern™ nano-S availablefrom Goffin-Meyvis. A sample can, for example, be prepared by additionof one drop of ink to a cuvette containing 1.5 mL ethyl acetate andmixed until a homogenous sample was obtained. The measured particle sizeis the average value of 3 consecutive measurements consisting of 6 runsof 20 seconds.

Suitable white pigments are given by Table 2 in [0116] of WO 2008/074548(AGFA GRAPHICS). The white pigment is preferably a pigment with arefractive index greater than 1.60. The white pigments may be employedsingly or in combination. Preferably titanium dioxide is used as pigmentwith a refractive index greater than 1.60. Suitable titanium dioxidepigments are those disclosed in [0117] and in [0118] of WO 2008/074548(AGFA GRAPHICS).

Also special colorants may be used, such as fluorescent pigments forspecial effects in clothing, and metallic pigments for printing a luxurylook of silver and gold colours on textiles.

If the colour pigment is included in the core of the capsule, apolymeric dispersant is advantageously used for dispersion stability andhandling during manufacturing of the capsules.

Suitable polymeric dispersants are copolymers of two monomers but theymay contain three, four, five or even more monomers. The properties ofpolymeric dispersants depend on both the nature of the monomers andtheir distribution in the polymer. Copolymeric dispersants preferablyhave the following polymer compositions:

-   -   statistically polymerized monomers (e.g. monomers A and B        polymerized into ABBAABAB);    -   alternating polymerized monomers (e.g. monomers A and B        polymerized into ABABABAB);    -   gradient (tapered) polymerized monomers (e.g. monomers A and B        polymerized into AAABAABBABBB);    -   block copolymers (e.g. monomers A and B polymerized into        AAAAABBBBBB) wherein the block length of each of the blocks (2,        3, 4, 5 or even more) is important for the dispersion capability        of the polymeric dispersant;    -   graft copolymers (graft copolymers consist of a polymeric        backbone with polymeric side chains attached to the backbone);        and    -   mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable dispersants are DISPERBYK™ dispersants available from BYKCHEMIE, JONCRYL™ dispersants available from JOHNSON POLYMERS andSOLSPERSE™ dispersants available from ZENECA. A detailed list ofnon-polymeric as well as some polymeric dispersants is disclosed by MCCUTCHEON. Functional Materials, North American Edition. Glen Rock, N.J.:Manufacturing Confectioner Publishing Co., 1990. p. 110-129.

The polymeric dispersant has preferably a number average molecularweight Mn between 500 and 30000, more preferably between 1500 and 10000.

The polymeric dispersant has preferably a weight average molecularweight Mw smaller than 100,000, more preferably smaller than 50,000 andmost preferably smaller than 30,000.

The pigments are preferably present in the range of 0.01 to 15%, morepreferably in the range of 0.05 to 10% by weight and most preferably inthe range of 0.1 to 5% by weight, each based on the total weight of theinkjet ink. For white inkjet inks, the white pigment is preferablypresent in an amount of 3% to 40% by weight of the inkjet ink, and morepreferably 5% to 35%. An amount of less than 3% by weight cannot achievesufficient covering power.

Generally dyes exhibit a higher light fading than pigments, but cause noproblems on jettability.

Dyes suitable for the inkjet ink include direct dyes, acidic dyes, basicdyes, solvent dyes and reactive dyes.

Suitable direct dyes for the ink-jet ink according to the presentinvention include C.I. Direct Yellow 1, 4, 8, 11, 12, 24, 26, 27, 28,33, 39, 44, 50, 58, 85, 86, 100, 110, 120, 132, 142, and 144; C.I.Direct Red 1, 2, 4, 9, 11, 134, 17, 20, 23, 24, 28, 31, 33, 37, 39, 44,47, 48, 51, 62, 63, 75, 79, 80, 81, 83, 89, 90, 94, 95, 99, 220, 224,227 and 343; C.I. Direct Blue 1, 2, 6, 8, 15, 22, 25, 71, 76, 78, 80,86, 87, 90, 98, 106, 108, 120, 123, 163, 165, 192, 193, 194, 195, 196,199, 200, 201, 202, 203, 207, 236, and 237; and C.I. Direct Black 2, 3,7, 17, 19, 22, 32, 38, 51, 56, 62, 71, 74, 75, 77, 105, 108, 112, 117,and 154.

Suitable acidic dyes for the ink-jet ink include C.I. Acid Yellow 2, 3,7, 17, 19, 23, 25, 20, 38, 42, 49, 59, 61, 72, and 99; C.I. Acid Orange56 and 64; C.I. Acid Red 1, 8, 14, 18, 26, 32, 37, 42, 52, 57, 72, 74,80, 87, 115, 119, 131, 133, 134, 143, 154, 186, 249, 254, and 256; C.I.Acid Violet 11, 34, and 75; C.I. Acid Blue 1, 7, 9, 29, 87, 126, 138,171, 175, 183, 234, 236, and 249; C.I. Acid Green 9, 12, 19, 27, and 41;and C.I. Acid Black 1, 2, 7, 24, 26, 48, 52, 58, 60, 94, 107, 109, 110,119, 131, and 155;

Suitable reactive dyes for the ink-jet ink include C.I. Reactive Yellow1, 2, 3, 14, 15, 17, 37, 42, 76, 95, 168, and 175; C.I. Reactive Red 2,6, 11, 21, 22, 23, 24, 33, 45, 111, 112, 114, 180, 218, 226, 228, and235; C.I. Reactive Blue 7, 14, 15, 18, 19, 21, 25, 38, 49, 72, 77, 176,203, 220, 230, and 235; C.I. Reactive Orange 5, 12, 13, 35, and 95; C.I.Reactive Brown 7, 11, 33, 37, and 46; C.I. Reactive Green 8 and 19; C.I.Reactive Violet 2, 4, 6, 8, 21, 22, and 25; and C.I. Reactive Black 5,8, 31, and 39.

Suitable basic dyes for the ink-jet ink include C.I. Basic Yellow 11,14, 21, and 32; C.I. Basic Red 1, 2, 9, 12, and 13; C.I. Basic Violet 3,7, and 14; and C.I. Basic Blue 3, 9, 24, and 25.

In a preferred embodiment the dyes are disperse dyes. Disperse dyes arewater insoluble dyes and are the only dyes that dye polyester andacetate fibres. Such dyes are especially useful as they can easily beincorporated into the core of the capsules. A disperse dye molecule isbased on an azobenzene or anthraquinone molecule with nitro, amine,hydroxyl, etc. groups attached to it.

Suitable examples of disperse dyes include Disperse Red 1, DisperseOrange 37, Disperse Red 55, and Disperse Blue 3. These colorants can beused as a single component, or they can be mixed with more than onecolorant of the same or different types to enhance the image quality.

As disperse dyes to be used for the ink, known disperse dyes can beused, specifically including C.I. Disperse Yellow 42, 49, 76, 83, 88,93, 99, 114, 119, 126, 160, 163, 165, 180, 183, 186, 198, 199, 200, 224and 237, C.I. Disperse Orange 29, 30, 31, 38, 42, 44, 45, 53, 54, 55,71, 73, 80, 86, 96, 118 and 119, C.I. Disperse Red 73, 88, 91, 92, 111,127, 131, 143, 145, 146, 152, 153, 154, 179, 191, 192, 206, 221, 258,283, 302, 323, 328 and 359, C.I. Disperse Violet 26, 35, 48, 56, 77 and97, C.I. Disperse Blue 27, 54, 60, 73, 77, 79, 79:1, 87, 143, 165,165:1, 165:2, 181, 185, 197, 225, 257, 266, 267, 281, 341, 353, 354,358, 364, 365, and 368, and the like, and dyes suitable to satisfyrequired hue and fastnesses in the application can be used.

For inkjet printing on textile sublimation, dye diffusion, and heatdisperse dye colorants are especially preferred because they have a highaffinity to certain synthetic polymeric or resinous materials.

Preferably a set of inkjet inks containing disperse dyes is used, forexample a CMYK inkjet ink set.

A preferred cyan inkjet ink (“C” ink) contains a disperse dye selectedfrom the group consisting of C.I. Disperse Blue 27, C.I. Disperse Blue60, C.I. Disperse Blue 73, C.I. Disperse Blue 77, C.I. Disperse Blue77:1, C.I. Disperse Blue 87, C.I. Disperse Blue 257, C.I. Disperse Blue367 and mixtures thereof.

A preferred magenta inkjet ink (“M” ink) contains a magenta disperse dyecolorant selected from the group consisting of C.I. Disperse Red 55,C.I. Disperse Red 60, C.I. Disperse Red 82, C.I. Disperse Red 86, C.I.Disperse Red 86: 1, C.I. Disperse Red 167:1, C.I. Disperse Red 279 andmixtures thereof.

A preferred yellow inkjet ink (“Y” ink) contains a yellow disperse dyecolorant selected from the group consisting of C.I. Disperse Yellow 64,C.I. Disperse Yellow 71, C.I. Disperse Yellow 86, C.I. Disperse Yellow114, C.I. Disperse Yellow 153, C.I. Disperse Yellow 233, C.I. DisperseYellow 245 and mixtures thereof.

A preferred black inkjet ink (“K” ink) contains a black disperse dye ora mixture of differently coloured disperse dyes chosen such that themixture is black in colour.

The inkjet ink set preferably contains other coloured inkjet inks, morepreferably at least one inkjet ink containing a disperse dye selectedform the group consisting of C.I. Disperse Violet 26, C.I. DisperseViolet 33, C.I. Disperse Violet 36, C.I. Disperse Violet 57, C.I.Disperse Orange 30, C.I. Disperse Orange 41, C.I. Disperse Orange 61 andmixtures thereof.

The pigments and/or dyes are preferably present in the range of 0.1 to20 wt % based on the total weight of the inkjet ink.

Optothermal Converting Agents

The inkjet ink, preferably the core of the capsules, may contain anoptothermal converting agent for the conversion of electromagneticradiation into heat when the inkjet printed image is exposed to aninfrared light source, such as a laser, a laser diode or a LED.

The optothermal converting agent may be any suitable compound absorbingin the wavelength range of emission by the infrared light source.

The optothermal converting agent is preferably an infrared dye as thisallows easy handling into the inkjet ink. The infrared dye may beincluded into the aqueous medium, but is preferably included in the coreof the capsule. In the latter, the heat transfer is usually much moreeffective.

Suitable examples of infrared dyes include, but are not limited to,polymethyl indoliums, metal complex IR dyes, indocyanine green,polymethine dyes, croconium dyes, cyanine dyes, merocyanine dyes,squarylium dyes, chalcogenopyryloarylidene dyes, metal thiolate complexdyes, bis(chalcogenopyrylo)polymethine dyes, oxyindolizine dyes,bis(aminoaryl)polymethine dyes, indolizine dyes, pyrylium dyes, quinoiddyes, quinone dyes, phthalocyanine dyes, naphthalocyanine dyes, azodyes, (metalized) azomethine dyes and combinations thereof.

The one or more optothermal converting agents are preferably present inthe range of 0.1 to 10 wt % based on the total weight of the inkjet ink.

Inkjet Printing Methods

An inkjet printing method according to a preferred embodiment of thepresent invention includes at least the steps of: a) jetting an inkjetink as described above on a substrate; and b) applying UV light to forma reaction product from the one or more chemical reactants in thecapsules.

In another preferred embodiment, the inkjet printing method includes atleast the steps of: a) jetting on substrates for pharmaceutical or foodpackaging an inkjet ink containing one or more UV curable chemicalreactants in a capsule have an average particle size of no more than 4μm; and b) applying UV radiation to form a reaction product from the oneor more UV curable reactive chemical reactants in the capsules, whereinthe capsule contains at least one photoinitiator, preferably a diffusionhindered photoinitiator, more preferably a polymeric or polymerizablephotoinitiator.

Food packaging is understood to include also packaging for liquids anddrinks like milk, water, coke, beer, vegetable oil and the like. Theinvention is advantageously used for providing food packaging,especially “primary” food packaging. Primary food packaging is thematerial that first envelops the product and holds it. This usually isthe smallest unit of distribution or use and is the package which is indirect contact with the contents. Of course, for reasons of food safety,the radiation curable compositions and inkjet inks may also be used forsecondary and tertiary packaging. Secondary packaging is outside theprimary packaging, perhaps used to group primary packages together.Tertiary packaging is used for bulk handling, warehouse storage andtransport shipping. The most common form of tertiary packaging is apalletized unit load that packs tightly into containers.

There is no real limitation on the type of substrate for inkjet printingone or more inkjet inks of the invention on. The substrates may haveceramic, metallic, glass, wood, paper or polymeric surfaces forprinting. The substrate may also be primed, e.g. by a white ink.

The substrate may be porous, as e.g. textile, paper and card boardsubstrates, or substantially non-absorbing substrates such as e.g. aplastic substrate having a polyethylene terephthalate surface.

Preferred substrates including surfaces of polyethylene, polypropylene,polycarbonate, polyvinyl chloride, polyesters like polyethyleneterephthalate (PET), polyethylene naphthalate (PEN) and polylactide(PLA) and polyimide.

The substrate may also be a paper substrate, such as plain paper orresin coated paper, e.g. polyethylene or polypropylene coated paper.There is no real limitation on the type of paper and it includesnewsprint paper, magazine paper, office paper, wallpaper but also paperof higher grammage, usually referred to as boards, such as white linedchipboard, corrugated board and packaging board.

The substrates may be transparent, translucent or opaque. Preferredopaque substrates includes so-called synthetic paper, like the Synaps™grades from Agfa-Gevaert which are an opaque polyethylene terephthalatesheet having a density of 1.10 g/cm³ or more.

There is no restriction on the shape of the substrate. It can be a flatsheet, such a paper sheet or a polymeric film or it can be a threedimensional object like e.g. a plastic coffee cup. The three dimensionalobject can also be a container like a bottle or a jerry-can forincluding e.g. oil, shampoo, insecticides, pesticides, solvents, paintthinner or other type of liquids.

In a preferred embodiment of the inkjet printing method, the substrateis selected from textile, glass, pharmaceutical and food packaging.

A major advantage of the current inkjet printing method is that not onlya wide range of textiles can be printed upon, but that after thefixation process (heat treatment) no post-treatments are necessary. Forexample, a classic washing process to remove dyes that are unfixed fromthe textile is not necessary. In addition, also many pre-treatments oftextiles can be avoided. For example, where classic inkjet printingprocesses require the application of a water-soluble polymer to thetextile prior to inkjet printing in order to prevent ink bleeding, thisis usually not necessary with inkjet inks containing capsules. Theavoidance of these pre- and post treatment speed-up and simplify themanufacturing of inkjet printed textiles, resulting in an economicalbonus. For example, no cumbersome ink swaps have to be performed in theinkjet printer, when changing the type of textile substrate. Also wastegenerated in the post-treatment can be avoided.

Suitable textiles can be made from many materials. These materials comefrom four main sources: animal (e.g. wool, silk), plant (e.g. cotton,flax, jute), mineral (e.g. asbestos, glass fibre), and synthetic (e.g.nylon, polyester, acrylic). Depending on the type of material, it can bewoven or non-woven textile.

The textile substrate is preferably selected from the group consistingof cotton textiles, silk textiles, flax textiles, jute textiles, hemptextiles, modal textiles, bamboo fibre textiles, pineapple fibretextiles, basalt fibre textiles, ramie textiles, polyester basedtextiles, acrylic based textiles, glass fibre textiles, aramid fibretextiles, polyurethane textiles (e.g. Spandex or Lycra™), Tyvek™ andmixtures thereof.

Suitable polyester textile includes polyethylene terephthalate textile,cation dyeable polyester textile, acetate textile, diacetate textile,triacetate textile, polylactic acid textile and the like.

Applications of these textiles include automotive textiles, canvas,banners, flags, interior decoration, clothing, hats, shoes, floor mats,doormats, brushes, mattresses, mattress covers, linings, sacking, stagecurtains, flame-retardant and protective fabrics, and the like.Polyester fibre is used in all types of clothing, either alone orblended with fibres such as cotton. Aramid fibre (e.g. Twaron) is usedfor flame-retardant clothing, cut-protection, and armor. Acrylic is afibre used to imitate wools.

The inkjet inks of the invention are also suitable for inkjet printingon leather.

Inkjet Printing Devices

The inkjet ink may be jetted by one or more print heads ejecting smalldroplets in a controlled manner through nozzles onto a substrate, whichis moving relative to the print head(s).

A preferred print head for the inkjet printing system is a piezoelectrichead. Piezoelectric inkjet printing is based on the movement of apiezoelectric ceramic transducer when a voltage is applied thereto. Theapplication of a voltage changes the shape of the piezoelectric ceramictransducer in the print head creating a void, which is then filled withink. When the voltage is again removed, the ceramic expands to itsoriginal shape, ejecting a drop of ink from the print head. However theinkjet printing method according to the present invention is notrestricted to piezoelectric inkjet printing. Other inkjet print headscan be used and include various types, such as a continuous type, athermal print head type and a valve jet type.

The inkjet print head normally scans back and forth in a transversaldirection across the moving ink-receiver surface. Often the inkjet printhead does not print on the way back. Bi-directional printing, also knownas multi-pass printing, is preferred for obtaining a high arealthroughput. Another preferred printing method is by a “single passprinting process”, which can be performed by using page wide inkjetprint heads or multiple staggered inkjet print heads which cover theentire width of the ink-receiver surface. In a single pass printingprocess the inkjet print heads usually remain stationary and thesubstrate surface is transported under the inkjet print heads.

Dryers and Pre-heating Devices

A dryer may be included in the inkjet printing device for removing atleast part of the aqueous medium. Suitable dryers include devicescirculating hot air, ovens, and devices using air suction.

A pre-heating device may be included in the inkjet printing device forheating the substrate prior to jetting. The pre-heating device may be aninfrared radiation source as described here below, or may be a heatconduction device, such as a hot plate or a heat drum. A preferred heatdrum is an induction heat drum.

A preferred pre-heating device uses Carbon Infrared Radiation (CIR) toheat the outside of the substrate, e.g. paper, quickly.

Another preferred pre-heating device is a NIR source emitting nearinfrared radiation. NIR-radiation energy quickly enters into the depthof the inkjet ink layer and removes water and solvents out of the wholelayer thickness, while conventional infrared and thermo-air energypredominantly is absorbed at the surface and slowly conducted into theink layer, which results usually in a slower removal of water andsolvents.

Infrared Radiation Sources

Infrared radiation may be emitted by an infrared radiation source (8) toopen up the capsules (3), i.e. by making the polymeric shell (4)permeable or even breaking it open in polymeric shell fragments.

An effective infrared radiation source (8) has an emission maximumbetween 0.8 and 1.5 μm. Such an infrared radiation source is sometimescalled a NIR radiation source or NIR dryer.

In a preferred form the NIR radiation source is in the form of NIR LEDs,which can be mounted easily on a shuttling system of a plurality ofinkjet print heads in a multipass inkjet printing device.

Curing Devices

The UV curing device emits UV radiation which is adsorbed by thephotoinitiator or photoinitiating system for polymerizing thepolymerizable compounds of the core.

The UV curing device may be a so-called cold UV lamp, such as UV LEDs,but may also emit so much heat radiation, e.g. a high or low pressuremercury lamp, that it is sufficient for removing water and organicsolvents in the inkjet printed image.

Alternatively, the inkjet printer may include only the drying unit forremoving water and organic solvents in the inkjet printed image, whilethe UV or thermal curing energy is applied afterwards, i.e. the UV orthermal curing means are located offline.

An inkjet ink containing UV curable reactive chemistry in the capsulescan be cured by exposure to ultraviolet radiation. The curing means maybe arranged in combination with the print head of the inkjet printer,travelling therewith so that the curing radiation is applied veryshortly after jetting. Preferably such curing means consists of one ormore UV LEDs because in such an arrangement, it can be difficult toprovide other types of curing means that are small enough to beconnected to and travelling with the print head. Therefore, a staticfixed radiation source may be employed, e.g. a source of curingUV-light, connected to the radiation source by means of flexibleradiation conductive means such as a fibre optic bundle or an internallyreflective flexible tube. Alternatively, the actinic radiation may besupplied from a fixed source to the radiation head by an arrangement ofmirrors including a mirror upon the print head.

However, it is not necessary to have the UV light source connected tothe print head. The source of UV radiation may, for example, also be anelongated radiation source extending transversely across the substrateto be cured. It may be adjacent the transverse path of the print head sothat the subsequent rows of images formed by the print head are passed,stepwise or continually, beneath that radiation source.

Any ultraviolet light source, as long as part of the emitted light canbe absorbed by the photoinitiator or photoinitiator system, may beemployed as a radiation source, such as a high or low pressure mercurylamp, a cold cathode tube, a black light, an ultraviolet LED, anultraviolet laser, and a flash light. Of these, the preferred source isone exhibiting a relatively long wavelength UV-contribution having adominant wavelength of 300-400 nm. Specifically, a UV-A light source ispreferred due to the reduced light scattering therewith resulting inmore efficient interior curing.

UV radiation is generally classed as UV-A, UV-B, and UV-C as follows:

-   -   UV-A: 400 nm to 320 nm    -   UV-B: 320 nm to 290 nm    -   UV-C: 290 nm to 100 nm.

In a preferred embodiment, the inkjet printing device contains one ormore UV LEDs with a wavelength larger than 360 nm, preferably one ormore UV LEDs with a wavelength larger than 380 nm, and most preferablyUV LEDs with a wavelength of about 395 nm.

Furthermore, it is possible to cure the image using, consecutively orsimultaneously, two light sources of differing wavelength orilluminance. For example, the first UV-source can be selected to be richin UV-C, in particular in the range of 260 nm-200 nm. The secondUV-source can then be rich in UV-A, e.g. a gallium-doped lamp, or adifferent lamp high in both UV-A and UV-B. The use of two UV-sources hasbeen found to have advantages e.g. a fast curing speed and a high curingdegree.

For facilitating curing, the inkjet printing device often includes oneor more oxygen depletion units. The oxygen depletion units place ablanket of nitrogen or other relatively inert gas (e.g. CO₂), withadjustable position and adjustable inert gas concentration, in order toreduce the oxygen concentration in the curing environment. Residualoxygen levels are usually maintained as low as 200 ppm, but aregenerally in the range of 200 ppm to 1200 ppm.

REFERENCE NUMERALS

Table A shows the reference numerals used in the drawings of FIGS. 1 to3.

TABLE A 1 Inkjet ink 2 Aqueous medium 3 Capsules 4 Polymeric shell 5Core 6 Inkjet printhead 7 Dryer 8 Infrared radiation source 9 UV curingdevice 10 Substrate 11 Pre-heating device 12 Ink droplet 13 Jetted inkdroplet 14 Colorant 15 Photoinitiator 16 Polymerizable compound 17Permeable polymeric shell 18 Polymerized compound

EXAMPLES

Measurement Methods

Surface Tension

The static surface tension of the radiation curable inks was measuredwith a KRÜSS tensiometer K9 from KRÜSS GmbH, Germany at 25° C. after 60seconds.

Viscosity

The viscosity of the inkjet ink was measured using a Brookfield DV-II+viscometer at 25° C. at 12 rotations per minute (RPM) using a CPE 40spindle. This corresponds to a shear rate of 90 s⁻¹.

UV Curing

The inventive radiation curable compositions and the comparativeradiation curable compositions were coated on a 300 μm aluminiumsubstrate using a bar coater and a 20 μm wired bar. All coated sampleswere cured were cured using a Fusion DRSE-120 conveyer, equipped with aFusion VPS/1600 lamp (D-bulb). The samples were cured using a belt speedof 20 m/min and at full power of the lamp. Each sample was passed fivetimes under the lamp.

Waterfastness

The waterfastness of a coated sample was tested by putting a water droponto the cured sample 30 minutes after curing the sample. One drop wasleft on the plate for 5 seconds and a second drop was left on the platefor 2 minutes. The drops were removed from the plate using a cotton pad,while putting pressure on the cotton pad. The visual damage of thecoating was evaluated and given a quotation of 0 to 5 according to thefollowing table.

TABLE Evaluation Observation 0 No visual damage 1 Change in surfaceglossiness 2 Coating damaged but no real removal 3 Removal of smallparts (<50%) of the coating 4 Removal of large parts (>50%) of thecoating 5 Complete removal of the coatingMaterials

All materials used in the following examples were readily available fromstandard sources such as Sigma-Aldrich (Belgium) and Acros (Belgium)unless otherwise specified. The water used was demineralized water.

Trixene™ BI7982 was supplied by Baxenden Chemicals LTD.

Takenate™ D110N was supplied by Mitsui Chemicals Inc.;

Dye-1 has been prepared according to the following procedure:

the synthesis of the aniline:

398.4 g (2.4 mol) potassium iodide was added to 400 ml dimethylacetamide. The mixture was heated to 65° C. and 329 g (2.4 mol)2-bromo-butane was added. The mixture was stirred at 70° C. for onehour. The mixture was heated to 78° C. and a mixture of 148.8 g (1.6mol) aniline and 310.4 g (2.08 mol) triethanol amine was added over twohours, while keeping the temperature at 78° C. The reaction was allowedto continue for three hours at 78-80° C. 800 ml water and 200 ml ethylacetate were added and the mixture was stirred for 15 minutes. Themixture was kept at 50° C. and the organic fraction was isolated. Theorganic fraction was washed twice with 400 ml water and all solventswere removed under reduced pressure at 75° C. 222 g of isobutyl anilinewas isolated (y: 93%, TLC analysis on TLC Silica gel 60F254, supplied byMerck, using methylene chloride as eluent: Rf: 0.5). The crude isobutylaniline was used without further purification. 36.6 g (0.24 ml)chloromethyl styrene, 30 g (0.20 mol) isobutyl aniline 32.3 g (0.25 mol)ethyl-di-isopropyl amine and 1 g (0.006 mol) potassium iodide weredissolved in 80 ml dimethyl acetamide. The mixture was heated to 100° C.and the reaction was allowed to continue for 2 hours at 100° C. Thereaction mixture was allowed to cool down to room temperature and pouredinto 1l water. The mixture was extracted with 200 ml methylene chloride.The organic fraction was isolated, dried over MgSO4 and evaporated underreduced pressure. The crude product was purified using preparativecolumn chromatography, on a Macherey Nagel Chromabond Flash column(MN-180 C18ec 45 μm D60 Å), using methanol as eluent. 29 g of thestyrene derivatised aniline was isolated (y: 55%, TLC analysis on TLCSilica gel 60F254, supplied by Merck, using hexane as eluent: Rf: 0.5).

the synthesis of dye-1:

13 g (0.08 mol) 2-amino-4-chlorothiazole-5-carbaldehyde (preparedaccording to Masuda et al., Bioorganic and Medicinal Chemistry, 12(23),6171-6182 (2004)) was dissolved in 100 ml phosphoric acid. The mixturewas cooled to 0° C. and 20 g of 40% solution of NO₂SO₃H in sulphuricacid was added, while keeping the mixture at 0° C. The reaction wasallowed to continue for one hour at 0° C. This solution was added to asolution of 21.2 g (0.08 mol) of the styrene derivatised aniline in 400ml of a 5% sulphuric acid solution in water and 150 ml methanol, whilekeeping the temperature at 0° C. The reaction was allowed to continuefor 30 minutes at 0° C. Dye-1 was isolated by filtration and washed witha mixture of water and methanol 1/1. The crude dye was redispersed inmethanol, isolated by filtration and dried. 25 g of Dye-1 was isolated(y: 71%, TLC analysis on Partisil™ KC18C, supplied by Whatman, usingMeOH/0.25 M NaCl as eluent: R_(f): 0.4).

Mackam™ 151C and Mackam™ 151L were supplied by Mcintyre Group LTD.

Lysine, glycerol, tetraethylene pentamine and triethanol amine weresupplied by Aldrich.

Olfine™ E1010 was supplied by DKSH.

Pionin™ C158 dry is the 100% compound obtained after evaporation of theethanol from Pionin-158, supplied by Takemoto Oil Fat Co. Ltd.

Omnipol™ TX is a polymeric thioxanthone supplied by IGM.

Omnipol™ 9210 is a polymeric α-amino-ketone Norrish type Iphotoinitiator supplied by IGM.

Genopol™ AB2 is a polymeric 4-dimethylaminobenzoic ester basedcoinitiator supplied by Rahn.

Ebecryl™ 130 is an aliphatic diacrylate supplied by CYTEC.

Dye-2 (CASRN1020729-04-7) has the following structure and can beprepared according to the methods disclosed in EP 427892 A (AGFA,

Mowiol™ 488 is a poly(vinyl alcohol) supplied by CLARIANT.

Alkanol™ XC is a surfactant (CAS 68442-09-1) from DU PONT.

Cab-o-jet™ 450 cyan pigment is a self-dispersible cyan pigmentdispersion available from CABOT.

Capstone™ FS3100 is a fluorosurfactant from DU PONT.

Tego Twin™ 4000 is a siloxane-based gemini surfactant from EVONIK.

Surfactant-1 is an amphoteric surfactant having the following structure:

Surfactant-1 was prepared according to the following procedure.

92 g (0.5 mol) dodecyl amine was dissolved in 30 ml1-methoxy-2-propanol. The mixture was heated to 50° C. and 43 g (0.5mol) crotonic acid was added. The mixture was heated to 120° C. for 18hours. After completion of the reaction, the mixture was allowed to cooldown to 80° C. and added slowly to 600 ml acetone. The mixture wasallowed to cool down to room temperature. Surfactant-1 was isolated byfiltration, washed with 300 ml acetone and dried. 106 g (yield=77%) ofsurfactant-1 was isolated. Surfactant-1 was analyzed, using LC-MS on anBruker Esquire-LC instrument. The structure of surfactant-1 wasconfirmed and no contamination was found. Surfactant-1 was furtheranalyzed using TLC chromatography on Partisil KC18F TLC plates suppliedby Whatman and using MeOH/water/0.5 M NaCl 9/0.5/0.5 as eluent.Surfactant-1 had an R_(f) of 0.6.

Surfactant-2 is an amphoteric surfactant, having the followingstructure:

Surfactant-2 was prepared according to the following procedure.

90 g (0.7 mol) octyl amine was dissolved in 54 g ethanol and the mixturewas heated to 60° C. 50 g (0.7 mol) acrylic acid was added and thereaction was allowed to continue for 16 hours at 75° C. The solvent wasremoved under reduced pressure and the oily residue was dissolved atreflux in 600 ml acetone. The mixture was cooled down to 15° C. andsurfactant-2 was allowed to crystallize over one hour. Surfactant-2 wasisolated by filtration, washed with 200 ml acetone and dried. 53 g ofsurfactant-2 was isolated (yield=37%). Surfactant-2 was analyzed, usingTLC chromatography on Partisil KC18F TLC plates supplied by Whatman andusing MeOH/water 9/1 as eluent. Surfactant-2 had an R_(f) of 0.69.

Example 1

This example illustrates the encapsulation methodology wherein UVcurable chemistry is encapsulated as nanocapsules into an inkjet ink.The encapsulated photoinitiators and co-initiators are of the polymerictype allowing inkjet printing of so-called low migration UV curableinkjet inks, for example, for food packaging applications.

Synthesis of Caps-1

1.8 g Omnipol™ TX, 1.8 g Genopol™ AB2, 3.5 g Omnipol™ 9210, 35 gEbecryl™ 130 and 11 g Takenate™ D110 N were dissolved in 32 g ethylacetate. This solution was added to an aqueous solution of 9.750 gMackam™ 151L, 3.25 g lysine and 0.121 Olfine™ E1010 in 63 g water anddispersed in the aqueous phase, using an Ultra-Turrax at 18000 rpm for 5minutes. An additional 44 g water was added and the pressure over themixture was gradually reduced to 150 mm Hg over 5 minutes. The ethylacetate was evaporated under reduced pressure (120 mm Hg) at atemperature of 50° C., followed by further reducing the pressure to 100mm Hg. After complete evaporation of all organic solvent and 25 g water,the mixture was further heated to 45° C. for 24 hours at ambientpressure. The mixture was allowed to cool down to room temperature andfiltered over a 30 μm filter. The particle size and particle sizedistribution was measured using a Zetasizer™ Nano-S (MalvernInstruments, Goffin Meyvis). The capsules had an average particle sizeof 404 nm.

Preparation and Evaluation of Inkjet Inks

The dispersion Caps-1 as prepared above was used for the formulation ofinkjet inks INV-1 and INV-2 as shown in Table 7. The weight percentage(wt %) of each component was based on the total weight of the ink.

TABLE 7 wt % of component: INV-1 INV-2 Caps-1 34.3 34.3 Cab-o-jet ™ 450cyan pigment 10 10 Glycerol 40 40 Capstone ™ FS-3100 0.45 — Tego ™ Twin4000 0.15 — Alkanol ™ XC — 1 Water 15.1 14.7

Inkjet ink INV-1 had a viscosity of 9.5 mPa·s and a surface tension of22 mN/m. Inkjet ink INV-2 had a viscosity of 8.7 mPa·s and a surfacetension of 30 mN/m.

The inkjet inks INV-1 and INV-2 were filtered over a 1.3 μm filter.

The jetting performance of the inkjet inks INV-1 and INV-2 was evaluatedusing a Dimatix™ DMP2831 system, equipped with a standard Dimatix™ 10 plprint head. The ink was jetted at 22° C., using a firing frequency of 5kHz, a firing voltage of 20 V-25 V, a standard waveform and a standardcartridge setting. Both inkjet inks INV-1 and INV-2 proved to have anexcellent jettability.

Example 2

This example illustrates the curing performance of an inkjet inkcontaining UV curable capsules

Preparation and Evaluation of Inkjet Ink INV-3

An inkjet ink INV-3 was formulated according to Table 8 using thecapsules Caps-1 of Example 1. The weight percentage of each componentwas based on the total weight of the inkjet ink.

TABLE 8 wt % of component: INV-3 Caps-1 90 Cab-o-jet 450 cyan pigment 10

The inkjet ink was coated on an aluminium plate using 20 μm wired bar,followed by a treatment specified in Table 9.

TABLE 9 Sample Treatment S-1 Drying at room temperature S-2 Drying atroom temperature followed by heating in an oven at 150° C. S-3 Drying atroom temperature followed by heating in an oven at 150° C. and UVcuring, using the method described above

The water fastness of each sample S-1 to S-3 was evaluated by putting adrop of water on top of the coated sample and leaving it on top of theplate covered with a glass beaker to avoid evaporation. After 30minutes, the water dropped was removed using a cotton pad and the damageto the coating was evaluated visually. The results are summarized inTable 10

TABLE 10 Sample Water fastness S-1 Complete removal of the coating S-2Complete removal of the coating S-3 No visual damage to the coating

From Table 10, it can be concluded that UV curing of INV-3 results inexcellent water fastness of the coating.

Example 3

This example illustrates the need for dispersing groups covalentlybonded to the polymeric shell, i.e. in order to have self-dispersingnanocapsules in the inkjet ink.

Synthesis of Self Dispersing Capsules Caps-2

1.8 g Omnipol™ TX, 1.8 g Genopol™ AB2, 3.5 g Omnipol™ 9210, 35 gEbecryl™ 130 and 11 g Takenate™ D110 N were dissolved in 32 g ethylacetate. This solution was added to an aqueous solution of 9.750 gMackam™ 151L, 3.25 g lysine and 0.121 Olfine™ E1010 and dispersed in theaqueous phase, using an Ultra-Turrax at 18000 rpm for 5 minutes. Anadditional 44 g water was added and the pressure over the mixture wasgradually reduced to 150 mm Hg over 5 minutes. The ethyl acetate wasevaporated under reduced pressure (120 mm Hg) at a temperature of 50°C., followed by further reducing the pressure to 100 mm Hg. Aftercomplete evaporation of all organic solvent and 25 g water, the mixturewas further heated to 45° C. for 24 hours at ambient pressure. Themixture was allowed to cool down to room temperature and filtered over a30 μm filter. The particle size and particle size distribution wasmeasured using a Zetasizer™ Nano-S (Malvern Instruments, Goffin Meyvis).The capsules had an average particle size of 404 nm.

Synthesis of Polymer Stabilized Caps-3:

1.8 g Omnipol™ TX, 1.8 g Genopol™ AB2, 3.5 g Omnipol™ 9210, 16 gEbecryl™ 130 and 30 g Takenate™ D110 N were dissolved in 32 g ethylacetate. This solution was added to an aqueous solution of 9.2 g Mowiol™488 and 0.12 g Olfine™ E1010 in 67.8 g water and dispersed in theaqueous phase, using an Ultra-Turrax at 20000 rpm for 5 minutes. 33 gwater was added and the pressure over the mixture was gradually reducedto 150 mm Hg over 5 minutes. The ethyl acetate was evaporated underreduced pressure (120 mm Hg) at a temperature of 50° C. An additional 25g of water was removed under reduced pressure. A solution of 2 gtetraethylene pentamine in 8 g water was added and the mixture washeated at 45° C. for 24 hours. The mixture was allowed to cool down toroom temperature and filtered over a 30 μm filter. The particle size andparticle size distribution was measured using a Zetasizer™ Nano-S(Malvern Instruments, Goffin Meyvis). The capsules had an averageparticle size of 320 nm.

Preparation and Evaluation of Inkjet Inks

The composition of the inventive inkjet ink INV-4 and comparative inkjetinks COMP-1 and COMP-2 are given in Table 11. The weight percentage (wt%) of each component was based on the total weight of the ink.

TABLE 11 wt % of component: INV-4 COMP-1 COMP-2 Caps-2 87.5 — — Caps-3 —17 34 Glycerol 9 50 33 Dye-2 0.5 0.5 0.5 Triethanol amine 2 1 2Alkanol ™ XC 1 1 1 Water — 30.5 29.5

The viscosity and the surface tension of the inks were measured, and theresults are summarized in Table 12.

TABLE 12 Surface tension Viscosity Inkjet Ink (mN/m) (mPa · s) INV-431.2 7.5 COMP-1 30.5 11 COMP-2 30.7 10.5

From Table 12, it should be clear that both the comparative inks COMP-1and COMP-2 and the inventive ink INV-4 are within the range forjettability.

All inks were filtered over a 1.6 μm filter before jetting. The jettingperformance of the inventive ink INV-4 and the comparative inks COMP-1and COMP-2 was evaluated using a Dimatix™ DMP2831 system, equipped witha standard Dimatix™ 10 pl print head. The ink was jetted at 22° C.,using a firing frequency of 5 kHz, a firing voltage of 20 V-25 V, astandard waveform and a standard cartridge setting.

Even with having a having a higher solid content, the inventive inkjetink INV-4 proved to be jettable, while none of the comparative inksCOMP-1 and COMP-2 were jettable.

Example 4

This example illustrates inkjet printing methods using mercury lamps andUV LEDs.

Synthesis of Caps-4

1.8 g Omnipol™ TX, 1.8 g Genopol™ AB2, 3.5 g Omnipol™ 9210, 31 gEbecryl™ 130 and 15 g Takenate™ D110 N were dissolved in 31 g ethylacetate. This solution was added to an aqueous solution of 3.5 g ofsurfactant-1, 0.6 g of surfactant-2, 2.5 g lysine and 0.120 g Olfine™E1010 in 75 g water and dispersed in the aqueous phase, using anUltra-Turrax at 24000 rpm for 5 minutes. An additional 38.5 g water wasadded and the pressure over the mixture was gradually reduced to 150 mmHg over 5 minutes. The ethyl acetate was evaporated under reducedpressure (120 mm Hg) at a temperature of 50° C., followed by furtherreducing the pressure to 100 mm Hg. After complete evaporation of allorganic solvent and 25 g water, 1 g of lysine was added and the mixturewas further heated to 45° C. for 24 hours at ambient pressure. Themixture was allowed to cool down to room temperature and filtered over a30 μm filter. The particle size and particle size distribution wasmeasured using a Zetasizer™ Nano-S (Malvern Instruments, Goffin Meyvis).The capsules had an average particle size of 210 nm.

Evaluation and Results

Two samples were prepared by coating the dispersion Caps-4 on analuminium plate using a 10 μm wired bar and dried at 100° C. temperaturefor 2 minutes.

A first sample T-1 was cured using a conveyer equipped with a 395 nm 12W Phoseon LED at a belt speed of 10 m/min. The sample was passed 6 timesunder the UV LED.

A second sample T-2 was cured using a Fusion DRSE-120 conveyer, equippedwith a Fusion VPS/1600 lamp (D-bulb) at a belt speed of 10 m/min. Thesample was passed 3 times under the lamp at full power of the lamp.

After curing the waterfastness of samples T-1 and T-2 was tested. Theresults are shown in Table 13.

TABLE 13 Waterfastness Sample UV curing 5 seconds 2 minutes T-1 UV LED 45 T-2 Hg bulb 0 0

From Table 13 it becomes apparent that only the sample T-2 cured with aHg bulb emitting sufficient heat during UV exposure gives excellentwater fastness directly after curing. UV LEDs emit insufficient heat toopen the capsules.

What is claimed is:
 1. An inkjet ink comprising: an aqueous medium; andcapsules including a polymeric shell surrounding a core; wherein theaqueous medium includes one or more surfactants selected from the groupconsisting of fatty acid salts, ester salts of a higher alcohol,alkylbenzene sulphonate salts, sulphosuccinate ester salts and phosphateester salts of a higher alcohol, ethylene oxide adducts of a higheralcohol, ethylene oxide adducts of an alkylphenol, ethylene oxideadducts of a polyhydric alcohol fatty acid ester, and acetylene glycoladducts and ethylene oxide adducts thereof; the capsules are dispersedin the aqueous medium by a dispersing group covalently bonded to thepolymeric shell; the core includes a photoinitiator and one or morechemical reactants that form a reaction product upon application of UVlight; the capsules have an average particle size of no more than 4 μmas determined by dynamic laser diffraction; the photoinitiator is adiffusion hindered photoinitiator selected from the group consisting ofmultifunctional photoinitiators, oligomeric photoinitiators, polymericphotoinitiators, and polymerizable photoinitiators; and the dispersinggroup is selected from the group consisting of a carboxylic acid or saltthereof, a sulfonic acid or salt thereof, a phosphoric acid ester orsalt thereof, a phosphonic acid or salt thereof, an ammonium group, asulfonium group, and a phosphonium group.
 2. The inkjet ink according toclaim 1, wherein the polymeric shell includes a polymer selected fromthe group consisting of a polyamide, a melamine based polymer, apoly(urea-urethane) polymer, and copolymers thereof.
 3. The inkjet inkaccording to claim 1, wherein the one or more chemical reactants includea monomer, oligomer, or polymer that is curable by free radicalpolymerization or by cationic polymerization.
 4. The inkjet inkaccording to claim 3, wherein the monomer, oligomer, or polymer includesat least one acrylate group as a polymerizable group.
 5. The inkjet inkaccording to claim 1, wherein the photoinitiator is a polymericphotoinitiator or a polymerizable photoinitiator.
 6. The inkjet inkaccording to claim 5, wherein the photoinitiator includes a polymeric orpolymerizable thioxanthone.
 7. The inkjet ink according to claim 1,further comprising an optothermal converting agent.
 8. The inkjet inkaccording to claim 7, wherein the optothermal converting agent is aninfrared dye.
 9. The inkjet ink according to claim 1, further comprisinga colorant.
 10. The inkjet ink according to claim 1, wherein the aqueousmedium includes a polymeric latex particle.
 11. The inkjet ink accordingto claim 1, wherein the polymeric shell is crosslinked.
 12. An inkjetprinting method including the steps of: jetting an inkjet ink accordingto claim 1 on a substrate; and applying UV light to the inkjet inkjetted on the substrate to form a reaction product from the one or morechemical reactants in the capsules.
 13. The inkjet printing methodaccording to claim 12, wherein the substrate is a textile, leather,glass, pharmaceutical packaging, or food packaging.
 14. The inkjetprinting method according to claim 13, wherein the step of applying UVlight is performed using UV LEDs with a wavelength larger than 360 nm.